Conventional colour photographic silver halide materials are processed by a process which includes a colour development step. In this step silver halide is reduced to metallic silver in the light-exposed areas and the oxidised colour developer formed in This reaction then couples with a colour coupler and forms image dye. The amount of dye produced is proportional to the amount of silver halide reduced to metallic silver.
Redox amplification processes have been described, for example in British Patent Specifications GB-A-1 268 126, GB-A-1 399 481, GB-A-1 403 418 and GB-A-1 560 572. In such processes colour materials are developed to produce a silver image (which may contain only small amounts of silver) and then treated with a redox amplifying solution to form a dye image. The redox amplifying solution contains a reducing agent, for example a colour developing agent, and an oxidising agent which is more powerful than silver halide and which will oxidise the colour developing agent in the presence of the silver image which acts as a catalyst. Oxidised colour developer reacts with a colour coupler (usually contained in the photographic material) to form image dye. The amount of dye formed depends on the time of treatment or the availability of colour coupler rather than the amount of silver in the image as is the case in conventional colour development processes. Examples of suitable oxidising agents include peroxy compounds including hydrogen peroxide, cobalt (III) complexes including cobalt hexammine complexes, and periodates. Mixtures of such compounds can also be used.
Since the amplifying solution contains both an oxidising agent and a reducing agent it is inherently unstable. That is to say unlike a conventional colour developer solution, amplifier solutions will deteriorate in a relatively short time even if left in a sealed container. The best reproducibility for such a process has been obtained by using a "one shot" system, where the oxidant is added to the developer and the solution mixed and used immediately (or after a short built in delay) and then discarded. This leads to the maximum solution usage possible with maximum effluent and maximum chemical costs. As a result the whole system is unattractive especially for a minilab environment where minimum effluent is required. It is believed that it is these shortcomings that have inhibited commercial use of this process.
Japanese Specification 64/44938 appears to describe such a system in which a silver chloride colour material is processed in a low volume of a single-bath amplifier solution. The processes described therein however fall short of what is required in the fully commercial environment for exactly the reasons given above.
WO-A-91/12567 (corresponding to British Patent Application No. 9003282.2) describes a method and apparatus for photographic processing in which a minimum amount of processing solution can be used in a processing tank which is thin and has a low volume. In order to overcome the inherent deterioration problem due to the instability of the processing solutions used, the method and apparatus described result in the need for high recirculation and/or replenishment rates. However, problems associated with non-uniform processing of the photographic material may be encountered due to local differences in the concentration of the processing solution.
U.S. Pat. No. 4,512,645 discloses a tank arrangement for the processing of photographic material in which improved material transportation and chemistry circulation are provided. This is achieved by having a tank with an integrally formed round bottom with a hollow contoured tank divider. The tank divider has an inlet port through which processing solution is added. A plurality of apertures are formed along the length of the divider through which processing solution is applied to the emulsion surface of the material being processed. Processing solution is discharged from the tank via an overflow port. In this arrangement, contact between the emulsion surface of the material and the walls of the tank is reduced due to the concave shape of the tank divider. This concave shape also allows processing solution to be circulated within the tank prior to its discharge via the overflow port.
However, the tank arrangement described in U.S. Pat. No. 4,512,645 requires a relatively large amount of processing solution to be present in the tank, and there is no recirculation of the solution. Such an arrangement, however, is unsuitable for use with unstable processing solutions as discussed above.
One problem associated with continuous processing in a tank having a low volume (typically 100 ml for a tank having a thickness of 1.5 mm, a width of 125 mm and a path length of 550 mm), is to obtain sufficient agitation of the processing solution. This problem arises because processing solution adheres to the emulsion surface of the material being processed and it is not removed (wiped off), and access of fresh processing solution to the emulsion surface is restricted in the narrow confines of the tank.
It is therefore an object of the present invention to improve access of processing solution to the emulsion surface of the material being processed, and as a result, provide more uniform processing of the photographic material.